Presby Environmental Inc. (PEI)

Advanced Enviro - Septic™ Wastewater Treatment System Septic Tank Effluent Filters and Charco al (Odor) Filters NOT Recommended


Courtesy of Courtesy of Presby Environmental Inc. (PEI)

Abstract: Effluent filters are installed in the outlet from the septic tank with the intended purpose of retaining solids inside the tank, preventing them from entering the treatment system and/or dispersal field. The concern is that if solids escape from the septic tank, they could cause clogging of the system components or the soil interface. While this may be a legitimate concern for some onsite systems, effluent filters can have a detrimental effect on Advanced Enviro-Septic (AES) technology1, therefore, they are not recommended by Presby Environmental (PEI) for the reasons explained below.

Effluent filters are subject to clogging and need frequent maintenance:
The biggest problem with most effluent filters is that they inevitably (and sometimes quickly) become clogged with the solids they are designed to capture. Many system owners are completely unaware of the ongoing maintenance requirements when an effluent filter is used; as a result, the filters tend not to receive the attention they require, and this lack of maintenance can have an adverse effect on the entire AES wastewater treatment system. Once the apparatus is clogged, it no longer functions as intended. In effect, the clogged filter creates a blockage in the connection between the septic tank and the treatment/dispersal field. Based on our years of troubleshooting experience, we have determined that clogged effluent filters are a common problem that often results in system malfunction in those states where they are required or when utilized by the designer or installer contrary to PEI's recommendation. Unfortunately, clogging is not easy to detect; therefore, frequent monitoring and ongoing preventive maintenance of the filter must be performed by the system owner.

Effluent filters can interfere with oxygen supply to the AES System:
When an onsite system is subjected to exceptionally heavy use in a short period of time, this is referred to as 'flash loading.' For example, when a three-bedroom house hosts a family reunion weekend, multiple houseguests and visitors would be using the plumbing facilities; as a result, the water used would far exceed the system's daily design flow. Flash loading can also create problems for effluent filters. An excessive volume of water enters the system faster than a partially-blocked filter can handle. This causes the septic tank to fill up quickly, which causes the 'scum' layer (accumulated solids and grease that float on the surface of the wastewater in the septic tank) to rise above the level of the effluent filter. If the overuse is of sufficient volume, wastewater may start to back up into the interior plumbing fixtures. When the home's usage returns to normal levels, the water level in the tank decreases, and the scum layer also recedes. However, some scum may end up lodged on top of the effluent filter in the process, blocking the flow of air through holes in the top. In this scenario, the system owner is likely to be completely unaware of the blockage; since only the top of the filter is blocked, the filter continues to allow water to pass from the septic tank to the treatment field, and the system would appear to be operating normally. However, with the top of the effluent filter blocked, oxygen supply to the system is disrupted, which in essence may cause the system to slowly suffocate. Some effluent filter designs do not feature a ventilated top, meaning air will never pass through, regardless of whether the filter is clogged or not.

A recent study by researchers at the University of California Davis examined how effluent filters affect the oxygen flow to septic systems {Evaluation of Greenhouse Gas Emissions from Septic Systems, 2010, Leverenz, et al.) The researchers concluded that when no effluent filter is used, an average passive system receives 150 to 400 cubic meters of air flow per day. However, when an effluent filter is used, air flow was found to be much less, in the range from 10 to 70 cubic meters per day. This means that the use of an effluent filter was determined to reduce the air flow quite significantly—in excess of 80%--even if the filter is not blocked or clogged.

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